Iran's Press Supervisory Board has suspended a hardline newspaper and cautioned two other outlets for criticizing last month's nuclear deal with world powers — a rare move for a body more used to upholding social conservatism.

The board suspended 9 Dey, a weekly newspaper that accused Tehran's negotiators of overstepping Supreme Leader Ayatollah Ali Khamenei's red lines in the negotiations, and referred its case to a court, the ISNA news agency reported on Monday.

Censors also cautioned Kayhan, an influential conservative daily, and the Raja News website, in a setback for critics who assert that Iranian negotiators made too many concessions to reach the historic deal on July 14.

The pact has been the subject of intense debate in the Islamic Republic, and President Hassan Rouhani took to the airwaves on Sunday evening to talk up the achievements of Iranian diplomats.

Iran's President Hassan Rouhani arrives for an address to the nation after a nuclear agreement was announced in Vienna, in Tehran, Iran, July 14, 2015.

Conservative newspapers have been targeted in the past: in February 2014 the Supreme National Security Council sued a conservative journalist working for Vatan-e Emrooz (Today's Nation) for criticising Rouhani's foreign policy.

But Iranian censors are more used to chasing publications perceived to be undermining the Islamic Republic's strict religious codes.

Most recently, censors in April banned monthly magazine Zanan-e Emrooz (Today's Women) for running an issue on "white marriage", a term used for unmarried couples living together in defiance of a law against extramarital sex.

The Committee to Protect Journalists (CPJ) listed Iran as the world's 7th most censored country in its 2015 annual report, noting the situation "has not improved under Rouhani despite the hopes of U.N. member states and human rights groups."